Metal foam and method for making



'May 9, 1961 J. c. ELLIOTT 2,983,597

METAL FOAM AND METHOD FOR MAKING Original Fil ed March 19, 1956 INVENTOR.

JOHV C. ELLIOTT BY Attorney Patented May 9, 1961 Fire 2,983,597 METAL FOAM AND METHOD FOR MAKING John C. Elliott, Anaheim, Calif, assignor, by mesne assignments, to Lot Corporation, Enid, Okla, a corporation of Delaware Continuation of application Ser. No. 572,423, Mar. 19, 1956. This application June 11, 1959, Ser. No. 819,558

83 Claims. c1. 7-5-40 The invention relates to metal foams and to methods for their production.

An object of this invention is to provide a quick and economical method of producing metal foams.

Another object is to provide a closed cell metal body having improved physical characteristics.

Another object is to provide a metal body of improved structural strength having an apparent specific gravity of less than 1.

abandoned, which was a continuation-in-part of my application Serial No. 250,346, filed October 18, 1951, now Patent 2,751,289.

Figure 1 is a partially cross-sectional view of a block of metal foam according to the invention;

Figure 2 is a cross-sectional view of a device for carrying out the process;

@Figure 3 is a longitudinal sectional view of another device for carrying out the process of this invention; and

Figure 4 is a cross-sectional view of the nozzle end of the device of Figure 3 provided with an induction heating loop.

Referring to \Figure l, the slab or body is predominantly composed of a metal 11 having dispersed throughout bubbles 12 of a gas and containing small particles 13 of a solid, preferably a metal. Such small particles while desirably of macro size as shown in the drawing, may, in some instances be dispersed in molecular size becoming a homogeneous part of the matrix metal.

In carrying out the process of the invention, a solid which decomposes on heating to form a gas is mixed into a molten metal to produce a wetting of the solid by the metal.

The mixing may be carried out at a temperature lower than the decomposition temperature of the gas-forming solid, in which case the temperature is raised or the pressure in the system lowered to bring about gas release and of the matrix metal so that the foam may be readily solidified before it comes dissipated. This may be accomplished by suitable choice of gas-forming agent and metal, or by controlling the pressure. One means of accomplishing this is to add a gas-forming solid to a metal -which'becomes molten at below the decomposition temperature of the solid, grind the solid with the molten metal to get good contact and wetting by the molten metal, and then add to this mixture another molten metal compatible with it which melts at slightly above the decomposition temperature of the solid so that on mixing the molten compositions there will be decomposition and foam at a temperature only slightly above the solidification temperature of the molten mixture. Another method is to add the gas-former to molten metal under such pressure that decomposition does not take place, maintaining the temperature at only slightly above the solidification temperature, and then release the pressure.

The gas-forming solid is preferably a heat decomposable compound containing a metal of a type that forms an alloy with the metal to which the gas-forming solid is added, so that on decomposition of the solid into a gas and its metal there takes place an alloying of this metal with the matrix metal. This alloying action causes a speeding up of the decomposition and a more rapid formation of the metal foam, and may further cause a setting or hardening of the foam Walls, thus counteracting their premature coalescence.

Excellent results are also obtained by mixing the hydride molten metal mixture with the second molten metal without allowing the hydride molten metal mixture to congeal or solidify prior to its addition to the second molten metal. This mixing of the two compositions Without prior solidification of the composition containing the hydride gives a finer structure of foam alloy than would otherwise be obtainable. It also makes it possible to readily obtain as much as 25% or more of hydride in the metal.

It is important that the gas-forming solid be made to wet the metal matrix to which is is added. It is found that grinding of the gas-forming solid in the molten metal brings about this wetting action. The ease of obtaining wetting also depends upon the choice of gas- .forming solid and molten metal to which it is added.

Thus good wetting and particularly satisfactory high strength, low density metal foams have been obtained by grinding powdered titanium hydride (TiH into molten aluminum, magnesium, or aluminum magnesium alloys; also by grinding zirconium hydride (ZiH into aluminum magnesium alloys ranging from aluminum to 80% magnesium. The use of titanium or zirconium hydrides with aluminum magnesium in the process of this invention has the further advantage of improving the grain structure of the alloy. I have also been able to foam aluminum, as shown in Example III below; and also 100% magnesium in analogous manner. With the latter metal an inert atmosphere is particularly essential to prevent ignition.

Other gas-formers and other metals may be used, although in some cases more extensive grinding to obtain wetting may be required to obtain good results and pressure changes may be called for. in order to obtain the preferred rapid decomposition at temperatures close to the melting point of the matrix metal. Thus barium hydride, lithium hydride, lithium aluminum hydride may be used as gas-formers by simply increasing the pressure to prevent decomposition before the metal to which they are added becomes molten. Thus powdered lithium aluminum hydride may be added to and ground in an aluminum magnesium eutectic composition at 10 atmospheres pressure, the temperature brought to slightly over the solidification point, and then the pressure released with resultant rapid decomposition of the hydride and formation of foam. Also it must be borne in mind that there is a time element for decomposition so that with fast work even without pressure control a gas-forming agent can be used to produce foam up to 350 C. or more above its initial decomposition point. This is important in considering the use of the following alternative gasformers for foaming:

Decomposition point, C.

Aluminum sulfate 770 Calcium carbonate 825 Zinc sulfate 740 Barium hydroxide 100 Copper pthalocyanin Approx. 425 Polymethyl siloxane Approx. 450 o-Tolyl phosphate Approx. 420 Alizarin Above 430 Tetraphenyl methane Above 435 Chrysen Above 450 Picene Above 470 Di-Z-naphthylamine Above 470 Oxarnide 419 1 methyl uric acid 400 Sodium'benzene sulfonate 450 Indanthrene "470 Gas-formers other than the metal hydrides and the others above mentioned may be used, the preferred ones being those which readily wet the metal matrix and which decompose at normal atmospheric pressure at temperatures not more than a few degrees above the melting point of the metal, although as above pointed out compounds having higher dissociation temperatures may be used. Examples of other suitable gas-forming compounds are copper phthalocyanin, organic silicon derivatives, and other silicon-containing compounds which on heating decompose.

The amount of gas-forming solid used may be varied Widely according to the amount of foaming and density of the final product desired. Particularly satisfactory high strength, low density light metal foams have been obtained using 8 through 10% of the hydride on the weight of the metal matrix. However, foamed metal may be obtained with /2% and less of hydride. Above 50% of hydride is generally not practical and at above 25% there is appreciable loss of strength and some embrittlement.

The temperature of the molten metal is preferably maintained during the mixing and decomposition of the hydride at close to the solidification point both because a higher temperature would require more rapid and greater cooling in order to solidify the molten foam before dissipation of the gas but also because the higher the temperature the more rapid the dissociation of the hydride and the greater tendency for non-uniform and large gas spaces.

The gas-former is preferably added to the molten metal in powdered form. The-size of the particle is not particularly important, the smaller particle, however, giving greater speed of dissociation due to greater surface area. Furthermore, the small particles give small metal particles which more readily disperse and where soluble in the base metal, more readily dissolve in this metal.

The grinding of the solid gas-former in the molten metal may be done in various ways. A steel roller heated to the temperature of the surrounding molten metal containing the solid-gas-former may be used. Also ball milling of the composition can be carried out to give the grinding action and resultant wetting of the gas-former by the molten metal. The term grinding as used in the specification and claims is used in the generic sense to include any wiping action under substantial pressure. Other means of el'fecting wetting of the solid gas-former by the molten metal may be used such as, for example, intensive mixing such as high speed mixing and the like.

While it is not desired to be restricted to any theory,

the following is a theory which conforms with the facts much-as pigment is dispersed in paint.

As the hydride becomes heated to the temperature of its dissociation there is a rapid formation of gas which is particularly rapid when the metal of the hydride is of the type which alloys with the other metal, and there is an apparent increase in viscosity similar to that in which the apparent viscosity of cream is increased when it is whipped. This apparent increase in viscosity is due to the entrapped gas producing a molten metal foam which on cooling becomes the solid metal foam of this invention.

The molten foam may be poured into molds and cast into various shapes although it is preferred to generate the foam within the mold. Sheets of foamed metal may be made by feeding a premixed and Wetted hydride molten metal mixture to a heated moving belt or through a series of heated rollers which bring about decomposition of the hydride and the formation of a sheet of foam which is then quenched to give a solid metal foam sheet.

The solid metal foam may vary greatly in strength and apparent specific gravity, depending upon the type of metal used and upon the size and extent of the gas bubbles which, in turn depends uponthe amount of gasformer used, the temperature during dissociation and the rapidity of cooling the molten foam. The gas bubbles or cells may vary from one-sixteenth inch and less to one inch and more in diameter. With light metals, apparent specific gravities of less than 1 are readily attained.

The foam metal bodies of this invention are particularly useful for the manufacture of boats, life preservers, and other light weight, strong articles.

The following examples are used to illustrate this invention:

Example I Powdered Til-I of a fineness such that most of the powder would pass through a 325 mesh screen, was added to a molten alloy consisting of by weight aluminum and 20% magnesium at a temperature of 600 C. to give a mixture containing 10% by weight of TiH The powdered Til-I was ground into the molten alloy by means of a heated steel pestle, the composition being maintained at the temperature of 600 C. This produced a molten foam which was then poured into a mold and allowed to cool and solidify. The resultant product was a closed cell metal body consisting of a dispersion of hydrogen bubbles of approximately one-quarter inch diameter in a solid matrix of the aluminum magnesium alloy containing minute particles of dispersed titanium metal alloyed at their interface with the aluminum magnesium.

Example II Sixty grams powdered zirconium hydride was ground into 60 grams of a low melting eutectic alloy of magnesium and zinc having a melting point of 341 C. This composition containing the ground and wetted zirconium hydride was allowed to cool and solidify. Five grams of the above alloy were then mixed into 5 0 grams molten aluminum magnesium 10% alloy at a temperature of about 650 C. The mixture melted immediately and dispersed quickly in the aluminum magnesium alloy. There was a violent evolution of hydrogen gas with production of molten foam metal which was immediately cooled before dissipation of the foam foaming a solid metal foam.

Example III Eight percent of powdered zirconium hydride (particle size through 325 mesh) was ground into 92% of molten high purity (99.75%) aluminum at 670 C. The mixture was maintained at this temperature until maximum volume was attained by decomposition of the hydride (about 30 seconds) at which time it was quenched. A solid foam, having average cell size about inch diameter resulted.

The foregoing examples. illustrate. .the production of metal bodies having an apparent specific gravity of less than 1. Such bodies may be obtained by using magnesium, aluminum, lithium, or mixtures thereof as the major constituent of the composition. Other metals or increased proportions of other metals may be used with or in place of the light metals to produce heavier metal foam bodies.

The process may be carried out with various metals but has been used to particular advantage by grinding a heavy metal hydride such as zirconium hydride or titanium hydn'des into a molten magnesium aluminum eutectic alloy (54.6% Mg, 45.4 Al by weight, melting point 463 C.) at a temperature below the decomposition temperature of the hydride, for example below 600 C., and then immediately mixing the molten composition into molten aluminum at a temperature above the decomposition temperature of the hydride, for example, at 700 C. or by cooling the eutectic-hydride mixture and grinding it into solid particles.

Referring to Figure 2, the extruder mixer 21 may be equipped with a screw 22 adapted to force the mixture toward one end. This screw is actuated by a shaft 23 which is driven by driving means (not'shown) located at a sulficient distance from the device so as not to overheat the driving means. into the mixer under pressure through pipe 24. The eutectic and the hydride may be fed through tubes 28 and 29 into a cylindrical grinding device comprising a chamber 25 into which is closely fitted on a solid core 26 drive shaft 27 which may be provided with narrow spiral grooves for further propulsion of the mixture. Core 26 slightly tapers so as to have a wider clearance at one end near feed tubes 28 and 29 and a very narrow clearance atits end adjacent to the extruder.

The eutectic and hydride may each be fed into the device through tubes 28 and 29 by means of pressure which may be screw pressure in the case of the hydride,

-or hydrostatic air or screw pressure in the case of the eutectic, or any other means suitable for feeding under considerable pressure. However, if the rotating drum is corrugated or provided with a spiral groove, pressure is not necessary. The eutectic and the foaming agent are intimately intermingled and are then fed through the connecting pipe 30 into the extruder where they become intermixed with the main aluminum stream in the extruder. The temperature in the extruder is higher than in the eutectic foaming agent mix, so that foaming is effected either toward the orifice 31 of the extruder, or immediately upon leaving the extruder either because of pressure release or due to auxiliary heating means which may be resistance-volume heating, induction heating, or the like. The temperature of the extruder is maintained above the melting point of aluminum and the temperature of the hydride foamer mix is maintained at a temperature above the melting point of the eutectic or the alloy employed for carrying the hydride, the substantially below the temperature at which foaming begins with the particular foaming agent employed.

In order to provide a continuous process for producing boards, strips or the like of a foam predominantly comprising aluminum, I may utilize the apparatus shown in Figures 3 and 4.

I may feed through tube 41 as shown in Figure 3, a stream of melted aluminum into the machine, which is maintained by heating means, not shown, at a temperature of 700 C. The worm 42 is revolved by driving means 43 and a shaft 44. The shaft is sufiiciently long to prevent the driving means from being overheated from the temperature of the operating member. The aluminum, which has entered through tube 41, is intermixed with an intimate suspension of at least one hydride selected from the group consisting of titanium hydride and zirconium hydride in an aluminum magnesium alloy as described above, although by means of maintaining a hydrogen pressure in excess of fifteen Molten aluminum may be fed pounds during the mixing operation it is also possible to prepare a suspension of these hydrides in pure aluminum and use it in this form. For the sake of convenience, however, I prefer to employ an aluminum-magnesium mixture having a melting point below 600 C.

The molten aluminum magnesium hydride mixture may be fed into the device with a plunger, pressed in hydrostatically, or preferably forced in by means of an auxiliary screw 45 from a hopper 46. Screw 45 may be driven through a shaft 47 extending from driving means 48.

In order to effect the foaming I may proceed in either of two different manners. I may operate the driving means under hydrostatic pressure in such a fashion as to maintain within the machine a hydrogen pressure of at least fifteen pounds. In this case substantially no foaming will take place inside the machine, but the foaming will take place as the mix emerges from the machine when the pressure is thus released. At the point of emergence I may provide a nozzle 49 of the form it is desired to give the emergent foam. I may then pick it up on a moving steel belt, not shown, or other conveying means, and I may surround it with temperature-controlling means for maintaining a desired extent of pressure or temperature for the optimum cooling rates for the particular alloys employed.

According to the other embodiment, I may operate at lower pressure or no pressure, and run the equipment at a temperature as low as feasible without risk of solidifying the metal anywhere in the system. Thus there will be some incipient foaming within the metal, and this will sufficiently lower the conductivity of the metal aggregate as to permit effective induction heating. Thus the metal in which incipient foaming is taking place passes through the nozzle 49, through an induction heating loop 50,

shown in cross-section in Fig. 4. This raises the temperature of the metal to the point where vigorous foaming takes place, whereupon the foam is removed by means not critical and well known to the art. The same effect can be obtained by other forms of heating, such as electrical or electromagnetic heating, including resistance heating.

It is thus seen that the invention is broad in scope and is not to be restricted excepting by the claims, in which it is my intention to cover all novelty inherent in the invention as broadly as possible in view of the prior art.

I claim:

1. The method of producing a closed cell metal body having an apparent specific gravity of less than 1 which comprises intensively mixing a metal hydride into a molten metal selected from the group consisting of magnesium, aluminum, lithium and mixtures thereof, while maintaining the temperature of the mixture at above the melting point of the metal, thereby producing a molten metal foam, and cooling the molten metal foam to produce a solid.

2. The method of producing a metal foam which comprises mixing a metal hydride with a first molten metal at below the decomposition temperature of the hydride and then intensively mixing the resultant composition with a second molten metal alloyable with said first molten metal, said intensive mixing being at a temperature above the decomposition temperature of the hydride.

3. The process of producing a metal foam comprising intensively mixing a suspension of at least one substance selected from the group consisting of zirconium hydride and titanium hydride in a magnesium aluminum alloy melting below 600 C. with another metal substantially consisting of aluminum, maintaining the said mixture under a hydrogen pressure sutficient to substantially prevent the decomposition of said substance, suddenly re ducing said pressure to substantially atmospheric pressure and thereby suddenly expanding said mixture and producing metal foam therefrom.

4. The process of producing a metal foam comprising 7 intensively mixing a suspension'of at least'one substance selected from the group consisting of zirconium hydride and'titanium hydride in a magnesium aluminum alloy melting below 600 C. with another metal substantially consisting of aluminum, maintaining the said mixture under a hydrogen pressure suflicient to substantially prevent the decomposition of the said hydride, expelling the said mixture through an orifice beyond which the said counter-pressure no longer prevails, thereby causing the sudden expansion and foaming of the said metal.

5. The process of producing a metal foam comprising intensively mixing a suspension of zirconium hydn'de in a magnesium aluminum alloy melting below 600 C. With another metal substantially consisting of aluminum, maintaining the said mixture under a hydrogen pressure sufficient to substantially prevent the decomposition of the said hydride, expelling the said mixture through an orifice beyond which the said counter-pressure no longer prevails, thereby causing the sudden expansion and foaming of the said metal.

6. The process of producing a metal foam comprising intensively mixing a suspension of titanium hydride in a magnesium aluminum alloy melting below 600 C. with another metal substantially consisting of aluminum, maintaining the said mixture under a hydrogen pressure sufficient to substantially prevent the decomposition of the said hydride, expelling the said mixture through an orifice beyond which the said counter-pressure no longer prevails, thereby causing the sudden expansion and foaming of thesaid metal.

7. A method for making expanded metals, comprising the step of intensively mixing a stream of an aluminumcontaining alloy with another stream of an aluminumcontaining alloy comprising intimately dispersed therein a hydride selected from the group consisting of titanium hydride, zirconium hydride, and mixtures thereof, maintaining the said materials at a temperature below 1000" C. and a pressure of higher than fifteen pounds per square inch, and then advancing the said material through 8. A metal foam body comprising a metal matrix having distributed therethrough completely enclosed cells, wherein .at least 75% of the volume thereof is occupied by said bubbles, said cells having an average diameter less than an inch, said body having an apparent specific gravity less than 1, said body characterized by having metal particles from the decomposition of foaming agent dispersed through said metal matrix, between said cells.

9. The article of claim 8 further characterized by said metal particles being titanium.

10. The article of claim 8 further characterized by said metal particles being zirconium.

11. A metal foam body comprising a metal matrix having distributed therethrough completely enclosed cells formed by decomposition of a foaming agent wherein at least 75% of the volume thereof is occupied by said cells, said cells having an average diameter less than an inch, said body characterized by having metal particles resulting from decomposition of said foaming agent dispersed through said metal matrix, between said cells and at least partially alloyed therewith.

12. The article of claim 11 further characterized by said metal being titanium.

13. The article of claim 11 further characterized by said metal being zirconium.

14. The article of claim 11 wherein said metal dispersed therethrough is at least partly in molecular size and a homogeneous part of the matrix metal.

15. A metal foam body comprising a metal matrix having distributed therethrough completely enclosed cells formed by decomposition of a foaming agent wherein at least 75% of the volume thereof is occupied by said cells, said cells having an average diameter less than an inch, said body characterized by having metal particles resulting from decomposition of said foaming agent dis- 7 persed therethrough is at least partly in molecular size and a homogeneous part of the matrix metal.

19. The method of producing a metal foam body which comprises intensively mixing into molten metal a substance which decomposes and liberates gas when heated, and heating said substance to decompose it while it is immersed in said molten metal to produce molten metal foam, then cooling said molten metal foam to produce said body.

20. The method of claim 19 wherein said substance comprises a metal hydride.

21. The method of claim 19 wherein said substance comprises a metal carbonate.

22. The method of claim 19 wherein said substance comprises 'a metal sulfate.

23. The method of claim 19 wherein the intensive mixing and the heating are carried out while maintaining said metal and said substance under pressure to suppress forming of said molten metal foam and wherein said pressure is then released to provide said molten metal foam.

24. The method of claim 19 wherein said intensive mixing is carried out in a first supporting means and the product of said intensive mixing is then moved from said first supporting means to a second supporting means substantially prior to decomposition of said substance and prior to formation of said molten metal foam, and formation of the molten metal foam substantially takes place in said second supporting means.

25. The method of claim 23 wherein said substance comprises a metal hydride.

26. The method of claim 23 wherein said substance comprises a metal carbonate.

27. The method of claim 23 wherein said substance comprises a metal sulfate.

28. The method of claim 23 wherein said pressure is released by passing the product of said intensive mixing through an orifice from a space wherein said pressure is provided to a space free from said pressure.

29. The method of claim 28 wherein said substance comprises a metal hydride.

30. The method of claim 28 wherein said substance comprises a metal carbonate.

31. The method of claim 28 wherein said substance comprises a metal sulfate.

32. The method of claim 24 wherein said second supporting means is a mold.

33. The method of claim 24 wherein said second supporting means comprises continuous conveying means.

34. The method of claim 32 wherein said substance comprises a metal hydride.

35. The method of claim 32 wherein said substance comprises a metal carbonate.

36. The method of claim 32'wherein said substance comprises a metal sulfate.

37. The method of claim 33 wherein said substance comprises a metal hydride.

38. The method of claim 33 wherein said substance comprises a metal carbonate.

39. The method of claim 33 wherein said substance comprises a metal sulfate.

40. The method of continuously producing metal foam which comprises intensively mixing into a continuously moving quantity of molten metal a continuously moving quantity of a substance which decomposes and liberates gas-when heated, continuously heating said substance to decompose it While it is immersed in said molten metal to provide a continuously moving body of molten metal 42. The method of claim 40 wherein said substance comprises a metal carbonate. 7

43. The method of claim 40 wherein said substance comprises a metal sulfate.

44. The method of claim 40 wherein the intensive mixing and the heating are carried out while maintaining said metal and said substance under pressure to suppress foaming of said molten metal foam and wherein said pressure is then released to provide said molten metal foam.

45. The method of claim 36 wherein said heating is essentially by heat transfer to said substance from said molten metal.

46. The method of claim 41 wherein said substance consists essentially of a dispersion of a metal hydride in an alloy.

47. The method of claim 46 wherein said hydride is selected from the group consisting of titanium and zirconium and the alloy is an alloy of aluminum and magnesium.

48. The method of claim 45 wherein said substance comprises a metal hydride.

49. The method of claim 45 wherein said substance comprises a metal carbonate.

50. The method of claim 45 wherein said substance comprises a metal sulfate.

51. The method of claim comprises a metal hydride.

52. The method of claim comprises a metal carbonate.

53. The method of claim comprises a metal sulfate.

54. The method of claim 44 wherein said pressure is released by passing the product of said intensive mixing through an orifice from a space wherein said pressure is provided to a space free from said pressure.

55. The method of claim 54 wherein said substance comprises a metal hydride.

56. The method of claim 54 wherein said substance comprises a metal carbonate.

57. The method of claim 54 wherein said substance comprises a metal sulfate.

.58. The method of claim 40 wherein said intensive mixing is carried out in a first containing means and the product of said intensive mixing is then moved from said first containing means to a second containing means substantially prior to decomposition of said substance and prior to formation of said molten metal foam and formation of the molten metal foam substantially takes place in said second containing means. i

59. The method of claim 58 wherein said second containing means is a mold.

60. The method of claim 59. wherein said substance 44 wherein said substance 44 wherein said substance 44 wherein said substance comprises a, metal hydride.

61. The'method of claim 59 wherein said substance comprises ametal carbonate. r

62. The method of claim 59 wherein said substance comprises a metal sulfate.

63. The method of claim 58 wherein said second containing means comprises continuous conveying means.

64. The method of claim 63 wherein said substance comprises a metal hydride.

65. The method of claim 63 wherein said substance,

comprises a metal carbonate.-

' 66. Themethod of claim 63 whereinsaid substance comprises a metal sulfate. i

67. The method of making a metal foam body which comprises introducing molten metalinto an extruder having a worm screw rotatably operable therein and intensively with said molten'metal a substance which decomposes and liberates gas when heated by revolving said Worm screw to provide an intermixture, extruding said intermixture to thereby remove it fro-m said extruder, heating said substance to decompose it while it is immersed in said molten metal to provide molten metal foam, then cooling said molten metal foam to provide said body.

68. The method of claim 67 wherein said metal is essentially aluminum.

69. The method of claim 67 wherein said metal is essentially magnesium.

70. The method of claim 67 wherein said metal comprises aluminum and magnesium.

71. The method of claim 68 comprises metal hydride.

72. The method of claim 68 comprises a metal carbonate.

73. The method of claim 68 comprises metal sulfate.

74. The method of claim comprises a metal hydride.

75. The method of claim comprises a metal carbonate.

76. The method of claim comprises a metal sulfate.

77. The method of claim comprises a metal hydride.

78. The method of claim wherein said substance wherein said substance wherein said substance 69 wherein said substance 69 wherein said substance 69 wherein said substance 70 wherein said substance 70 wherein said substance comprises a metal carbonate.

79. The method of claim 70 wherein said substance comprises a metal sulfate.

80. The method of producing a metal foam body which comprises intensively mixing into molten metal a substance which decomposes and liberates gas when heated, and then heating said substance to decompose it while it is immersed in said molten metal to produce molten metal foam, then cooling said molten metal foam to produce said body.

81. The method of producing a metal foam body which comprises intensively mixing into molten metal a substance which decomposes and liberates gas when heated, while heating said substance to decompose it while it is immersed in said molten metal to produce molten metal foam, then cooling said molten metal foam to produce said body.

82. The method of continuously producing metal foam which comprises intensively mixing into a continuously moving quantity of molten metal a continuously moving quantity of a substance which decomposes and liberates gas when heated, then continuously heating said substance to decompose it while it is immersed in said molten metal to provide a continuously moving body of molten metal foam, and then continuously cooling said molten metal foam.

83. The method of continuously producing metal foam which comprises intensively mixing into a continuously moving quantity of molten metal a continuously moving quantity of a substance which decomposes and liberates gas when heated, while continuously heating said substance to decompose it while it is immersed in said molten metal to provide a continuously moving body of molten metal foam, and then continuously cooling said molten metal foam.

References Cited in the file of this patent 1 UNITED STATES PATENTS 1,633,258 Laise June 21, 1927 2,434,775 Sosnick Jan. 20, 1948 2,553,016 Sosnick May 15, 1951 2,661,238 Osti et a1 Dec. 1, 1953 2,751,289 Elliott June 19, 1956 r 2,935,396 Pashak May 3, 1960 FOREIGN PATENTS 615,147 France Dec. 30, 1926 811,814 Great Britain Apr. 15, 1 959 

1. THE METHOD OF PRODUCING A CLOSED CELL METAL BODY HAVING AN APPARENT SPECIFIC GRAVITY OF LESS THAN 1 WHICH COMPRISES INTENSIVELY MIXING A METAL HYDRIDE INTO A MOLTEN METAL SELECTED FROM THE GROUP CONSISTING OF MAGNESIUM, ALUMINUM, LITHIUM AND MIXTURES THEREOF, WHILE MAINTAINING THE TEMPERATURE OF THE MIXTURE AT ABOVE THE MELTING POINT OF THE METAL, THEREBY PRODUCING A MOLTEN METAL FOAM, AND COOLING THE MOLTEN METAL FOAM TO PRODUCE A SOLID. 